This claims priority to Japanese Patent Application No. 2000-110686, filed Apr. 12, 2000, the contents of which are incorporated herein in their entirety by reference.
1. Field of the Invention
The present invention relates to a plastic covering material having excellent shape keeping ability for sealing containers such as cup, bowl and tray formed of paper, synthetic resin and the like.
2. Description of the Prior Art
Conventionally, as materials for a covering material which is bonded to an opening of a container made of paper, synthetic resin and the like for accommodating beverages, portions, foods such as instant noodles, or medical devices such as disposable contact lens for sealing the container, aluminum foils and polypropylene polymers have been widely used.
The reason why aluminum foils are used in the covering material as described above is that in addition to shielding the light and air thereby protecting the contents, the covering material has ability to keep a turned-up shape (shape keeping ability) in the case where the covering material is partly torn off and then the contents are taken from the container or hot water is poured into the container.
As an alternative of such conventional covering materials having aluminum foil layer, a covering material formed of a plastic in its entirety has bean proposed. For example, in Japanese Unexamined Patent Publication JP 11-01810 A (1999), a covering material which is formed by punching a laminated material into a predetermined shape is disclosed, the laminated material being configured by laminating heat resistant films on both sides of a base material of a co-extruded film having a center layer made of high-density polyethylene and polypropylene-based polymer and coating layers made of high-density polyethylene on both sides of the center layer to make a lamination base material, and providing a sealant layer on the bottom surface of the lamination base material. However, such conventional plastic covering materials did not have sufficient shape keeping ability. That is, the ability of the conventional covering materials to keep the deformed condition when they are deformed, for example, by bending was not satisfactory. Furthermore, the conventional covering materials did not have sufficient shape recovering ability after deformation. That is, it was difficult for the conventional covering materials to recover the condition before deformation without causing damages such as folding or wrinkles.
It is an object of the present invention to provide a plastic covering material having excellent shape keeping ability and shape recovering ability after deformation.
As the result of researches for developing a plastic covering material having excellent shape keeping ability and shape recovering ability after deformation, the inventors of the present invention found that a covering material having a layer formed of a resin of which glass transition point is in the range of 10xc2x0 C. to 50xc2x0 C. satisfies the above-mentioned object and accomplished the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating referred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d, and variations such as xe2x80x9ccomprisesxe2x80x9d and xe2x80x9ccomprisingxe2x80x9d, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integer or step.